1. Field of the Invention
The invention is related to the field of communications and, in particular, to delivery of text messages.
2. Statement of the Problem
In many mobile networks, text messaging has become a very popular mode of communication. Short Message Service (SMS) is a communication protocol allowing the exchange of short text messages (i.e., 160 characters) between mobile devices. Often times, mobile users more frequently use text messaging for communication than voice calls.
Text messages are transmitted over signaling channels of a mobile network, such as over SS7 channels. An SMS Center (SMSC) in the mobile network has a store-and-forward system for delivering text messages to their destinations over the signaling channels. Upon initially receiving a text message, the store-and-forward system first stores (persistently) the text message, and then initiates a delivery attempt for the text message. If the delivery attempt is unsuccessful, then the store-and-forward system retries delivery after a time period (e.g., 10 minutes, 30 minutes, etc). The store-and-forward system will retry delivery a predefined number of times before the text message is discarded.
The following illustrates an example of delivering a text message from an originating mobile device to a destination mobile device in a UMTS network. To start, a sender originates the text message through the originating mobile device, and the originating mobile device sends the text message to an SMSC. A store-and-forward system in the SMSC receives and stores the text message. The store-and-forward system then queries a Home Location Register (HLR) to identify routing information for the text message. The HLR responds to the query with the routing information, and the store-and-forward system then attempts to forward the text message to the destination mobile device based on the routing information. If the first delivery attempt is unsuccessful, then the store-and-forward system retries delivery after a time period. The store-and-forward system will retry delivery a predefined number of times before the text message is discarded.
The store-and-forward approach to text messaging drives up the cost of the SMSC due to the expensive storage subsystems used for storing the text messages before delivery. As the volume of text messages increases in mobile networks, the unit price per text message drops significantly. Thus, profit margins for text messaging have become lower for the network operators. To reduce costs and increase network capability for delivering text messages, some network operators no longer use only store-and-forward processing. Instead, many network operators offer an alternative approach, which is referred to as First Delivery Attempt (FDA) processing. With FDA processing, delivery of a text message to the destination is attempted before it is stored. If delivery fails, then the text message is stored, and normal store-and-forward processing occurs.
The following illustrates an example of FDA processing used to deliver a text message in a UMTS network. The sender originates the text message through an originating mobile device, and the originating mobile device sends the text message to an FDA system. The FDA system initially receives the text message, and queries the HLR to identify routing information for the text message. The HLR responds to the query with the routing information, and the FDA system then attempts to forward the text message to the destination mobile device based on the routing information, without first persistently storing the text message in memory. If the FDA system determines that delivery of the text message failed, then the FDA system routes the text message to the SMSC. The store-and-forward system in the SMSC then stores the text message, and attempts delivery of the text message according to store-and-forward processing.
One problem encountered by network operators is that FDA processing may cause congestion in a mobile network in times of high traffic volume. The message queues in the FDA system are small, so when traffic volume is high the text messages may get delayed in the FDA system. This network congestion may result in failed delivery of text messages and lost revenue for the network operator.